35 



grouped together in a similar manner, it is probable that in their migra- 

 tion to positions near the periphery' of the eml)ryo sac those from one 

 group would come to occupy mainly one portion of the embryo sac, 

 while the others would occupy the other portion. This would lead to 

 the production of kernels where approximately half of the endosperm 

 resembles one parent and the other half the other parent, as was the case 

 in some kernels produced in Pedrick's Perfected Golden Beauty 9 X 

 Cuzco 7a $ (p. 21, PI. I, tig. 2-i) and Gilman Flint X StowelFs Ever- 

 green (p. 29). 



As bearing on this hypothesis it should be remembered that it is 

 well known that in the e.gg cell proper of both plants and animals the 

 male and female pronuclei do not fuse together intimately, but remain 

 more or less distinct until the reorganization of the .daughter nuclei 

 after the first division, and among certain animals the maternal and 

 paternal elements have been traced through several cell generations. 

 Hacker ^ first found that in Ckjclops drenmis the two pronuclei do not 

 fuse, but give rise to two separate groups of chromosomes, which lie 

 side by side at the equator of the tirst cleavage spindle, and in the 

 dauo"hter cells resultino- from this division each nucleus consisted of 

 two distinct lobes, which Hacker thought to represent the maternal and 

 paternal elements. The truth of this was later demonstrated by Riick- 

 ert," who was able to trace the distinct groups of chromosomes derived 

 from each parent, from the bi-lobed nuclei of the two-celled stage 

 through the second cleavage, and in mau}^ instances distinctly recog- 

 nized the double character of the nuclei in a much later stage, when 

 the germ layers were being formed. In the division of the bi-lobed 

 nuclei of the two-celled stage a double spirem and double group of 

 chromosomes are formed, the spindles being almost entirely distinct 

 and resulting in the formation of bi-lobed nuclei. In Ascaris also, 

 the maternal and paternal chromosomes remain distinct for some time, 

 according to Herla,^ who was able to distinguish them perfectly as 

 far as the twelve-cell stage. The male nucleus, furthermore, has been 

 found by a number of investigators to be capable of independent 

 division. This was shown in the now classical researches of Boveri* in 

 fertilizing enucleated fragments of the eggs of sea urchins. Boveri 

 showed that spermatozoa will enter enucleated fragments of eggs and 

 that such fragments divide and give rise to dwarf larvae, diliering 

 only from the normal in size and in containing only half the ordinary 



^Hiicker. Die Eibildung bei Cyclops und Canthoeamptus. Zool. Jahrb. V., 1892. 



^ Riickert. Ueber das Selbstiindigbleibeii der viiterlichen und miitterlichen Kern- 

 substanz wahrend der ersten Entwicklung des befruchteten Cyclops- Eies. Archiv. 

 f. mikroscop. Anatomie, XLV, 3. 1895. 



^'Herla. Etude des variations de la mitose chez I'ascaride megalocephale. Arch- 

 ives de Biologie, XIII. 1893. 



* Boveri. tJber die Befruchtungs und Entwickelungsfiihigkeit kernloser Seeigel- 

 Eier, etc. Archiv. f. Entwickelungsmechanik, II, 3. 1895. 



